Method for producing a pulp molding die



Dec. 11, 1962 w. H. STICKNEY ETAL 3,06

METHOD FOR PRODUCING A PULP MOLDING DIE Original Filed Dec. 20, 1956 3Sheets-Sheet 1 Dec. 11, 1962 w. H. STICKNEY ET AL 3,067,470

METHOD FOR PRODUCING A PULP MOLDING DIE Original Filed Dec. 20, 1956 5Sheets-Sheet 2 INVENTORS FIG.

Dec. 11, 1962 w. H. STICKNEY ET AL ,0

METHOD FOR PRODUCING A PULP MOLDING DIE Original Filed Dec. 20, 1956 5Sheets-Sheet 5 FIG.6 58

ATTORNEY United States Patent 3,067,470 METHOD FOR PRODUCING A PULPMOLDING DIE Wendell H. Stickney, Wilhraham, Mass., and Richard F.Reifers, Lincolnwood, Ill., assignors to Diamond National Corporation. acorporation of Delaware Original application Ser. No. 629,495, Dec. 20,1956, now Patent No. 2,981,330, dated Apr. 25, 1961. Divided and thisapplication May 6, 1960. Ser. No. 28,177

7 Claims. (Cl. 1855) The present invention relates to a method of makinga pulp molding die and more particularly to a method of making a porousdie suitable for use in producing pulp articles.

This application is a division of our copending applica tion Serial No.629,495 filed December 20, 1956, for Pulp Molding, which issued asPatent No. 2,981,330.

Heretofore, pulp molding dies have been made with a'woven wire clothmaterial stretched to conform to the die surface. The manufacture ofthis type of die has caused many difliculties due to the limited amountof distortion or stretching of which the wire cloth is capable to enableit to conform to the die surface. When the distortion of the woven wireis too great, it either tears or ruptures, or the mesh becomes sodistorted as to cause it to fail to function properly as a pulp moldingsurface. This difficulty is particularly prevalent in the manufacture ofdies for the making of pulp articles such as egg cartons and othercomplex designs.

It is therefore an object of the present invention to provide a novelmethod of making a pulp molding die that can be readily manufactured toconform to any desired design.

It is a further object of the present invention to provide a novelmethod of making a pulp molding die that is made up of a porous sinteredmaterial molded to the desired design.

Another object of the present invention is to provide a novel method ofmaking a pulp molding die that is made up without wire woven clothapplied thereto.

These and other objects and the nature and advantages of the instantinvention will be apparent from the following description taken inconjunction with the accompanying drawings, wherein:

FIG. 1 is a perspective view of a pulp molding die made in accordancewith the present invention;

FIG. 2 is a perspective view of the die with the contoured moldingsurface removed;

FIG. 3 is a perspective view of the metal plate and attached reinforcingstructure in inverted position over the male master pattern prior toapplication of the resin coated spherical particles;

FIG. 4 is a perspective view of the die shown in FIG. 1 in invertedposition;

FlG. 5 is a sectional view taken along the FIG. 1;

FIG. 6 is a perspective view of the male master pattern; and

FIG. 7 is a top plan view of an article molded from the die of FIG. 1.

Molding dies of the type disclosed herein are used to form or mold pulparticles from liquid pulp mixtures, these mixtures being composed offibers and some liquid, such as water, the liquid being drawn throughthe die, leaving a layer or coating of felted fibers on the moldingsurface. The article so formed is then removed from the molding surfaceand the process is repeated. The operation of the line 55 of pulpmolding dies is a well understood art, and it is believed unnecessary todiscuss their functions in greater detail.

The following description of the molding die and the 3,067,470 PatentedDec. 11, 1962 method of making it is described in conjunction with themolding of an egg carton having therein a plurality of pocket sectionswith a cover portion connected to this pocket section by a hingestructure which will enable it to be folded over, forming a closedcontainer. This egg carton is illustrated in FIG. 7 and comprises acellular compartmented bottom section, generally designated 10, to whicha non-cellular or open faced, tray-like cover section 11 is integrallyhinged by a longitudinal crease 12 at corresponding side margins of thesection. Cover section 11 has pairs of opposed end walls 13 and sidewalls 14 integrally joined by rounded corners 15, and a fiat top panel16 is likewise integrally joined about its periphery with the walls. Theexterior surface of this panel is smooth and continuous, suitable forthe reception of printed matter or ornamentation.

The cover section side walls are of scalloped shape featuringlongitudinally spaced, outwardly curved or recessed bays 17 to increasethe egg room in the cover section, which recesses are spaced byintervening, inwardly extending abutment portions 18. These portionscome into contact with the cellular bottom section 10 when the carton isclosed.

The interior of bottom section 10 is partially subdivided into two rowsof six egg receiving cells 19, by a longitudinally extending series ofupstanding center separator posts 20 which are of generally rectangularoutline at their tops.

An elongated internal cover bracing and locking flange 26 is integrallyhinged by a longitudinally extending crease 27 to the side margin ofbottom section 10 opposite its cover hinge 12. Flange 26, like the sidewalls of cover section 11, is of generally scalloped outline. It has eggaccommodating bays or recesses 28 which are in transverse alignment withbottom section egg cells 19. The locking means comprises a pair oflocking elements or lugs 30 which are integrally molded in the flange 26to project outwardly adjacent the free outer edge thereof, and detentapertures 31 molded in the front wall 14 immediately adjacent itsjunction with cover top panel 16.

In use, when the eggs have been deposited in the bottom cells 19, flange26 is swung to upstanding position adjacent the front row of eggs andthe cover section 11 is swung downwardly into externally telescopedrelation over the flange. As this occurs, the free front cover wall 14slides downwardly over the locking lugs 30 until the flange and coverare in interlocked relationship.

The die, in accordance with the present invention, is used for moldingthe egg carton described heretofore.

The die shown in FIG. 1, designated in its entirety by the numeral 40,includes a flat metal plate 42 prepared with a window opening 44 on thecenter thereof corresponding in shape to the outer periphery of the eggcarton. A plurality of holes 45 are provided in the plate 42 forattaching the finished die to a conventional die box. The plate 42becomes effective in use as a margin strap and also as a support for thecontoured molding surface. Attached to the underside of the plate 42 isa reinforcing structure or grid arrangement which may consist of aplurality of rods 46 supported at each end in a plate 48, each of whichis attached to the plate 42 by screws. A plurality of pedestal supports50 are arranged on the rods at equal intervals, each of which has aplurality of feet 52. Four feet 52 are illustrated on each support 50.The supports act to absorb any tendency for the molding die to collapseunder vacuum. The feet 52 rest on the platen of the main Wet endcylinder of the molding apparatus.

To form the contoured molding surface of the die, a male master mold orpattern 54 is utilized. This master mold or pattern 54 is illustrated inFIGS. 3 and 6. This mold or pattern may be made of plaster or metal andU conforms to the shape of the article to be molded when in the fiatposition.

To make the desired pulp molding die 40, the metal plate 42 with itsattached grid arrangement is inverted and placed over said male mastermold or pattern 54 so that the window opening 44 in the plate ispositioned to fit over the periphery of the pattern 54 with the contoursin the pattern extending upwardly through the window opening 44 betweenthe rods 46 and the pedestal supports50 of the grid arrangement, asshown in FIG. 3. Side plates 55 are attached at each side to the plates48, whereby the entire pattern is enclosed.

For ease in removal after the molding of the die, the male master orpattern 54 may be coated with a silicone resin and baked. The siliconeacts as a release agent during the'molding. I p

The molding material 58, which has been previously prepared, is pouredover the pattern 54 until the pattern is completely covered and themolding material reaches the height of the plates 48 and 56, as shown inFIG. 4. The entire mold is vibrated during the pouring of the moldingmaterial.

The molding material 58 is made up of a plurality of small sphericalparticles having a diameter of approximately 3 to 50 mils, preferably inthe range of 830 mils. These particles may be small glass beads whichare spheres" of an approximate diameter of 15 mils, metal powders whichare spherical particles of a diameter of 1-5 to 25 mils,sphericalsand-particles-of similar diameter or other sphericalparticles. The spherical particles are coated with a phenolic resin anddried to yield a freely pourable coated powder.

After the coated spherical particles have been poured into the mold andvibrated sufliciently to fill all crevices,

the mold is placed in an oven and heated to a temperature of about 350F. for several hours. After cooling to room temperature; the resultingdie is removed from the pattern 54. This die, which is illustrated inFIG. 1, has a porous resin-sintered spherical particle structure whereinthe spherical particles are bonded together at portions of theirperipheries by the cured resin leaving voids and pores for the passageof liquid during the pulp molding operation.

A specific example of the treatment of the spherical particles and themolding and curing of a die is as follows: One hundred parts by weightof spherical glass beads having a diameter of .015 inch are placed in amixer and a mulling mix action is started. Slowly three-fourths part byweight of a liquid phenol-formaldehyde bonding resin is added to themixer. When the mixture is complete four parts by weight of a drypowdered phenolformaldehyde resin are added slowly until the mixturehasbecome complete and uniform. The resulting coated beads should be dryenough to pour freely. The coated particles are now poured into the moldas illustrated in FIGS. 3 and 4, while vibrating the entire mold. Thepattern has previously been treated with a silicone and baked to providea release agent. The mold is placed in an oven and the resin is cured byheating at 150 for two hours. The temperature is increased in incrementsof 20 F. for ten hours until a temperature of 350 F. is reached. Thetemperature is held at 350 F. for two hours. The mold is removed fromthe oven and allowed to cool to room temperature. The die is now removedfrom the pattern and is ready for use in pulp molding.

A second example of this method is as follows: 2000 cc. of bronzepowder, approximately spherical in shape and about .018 inch in diameterwas placed into a muller mixer. The composition of the metal powder isnot critical, however, the bronze powder used here contained 95.5%copper coated with 4.5% tin. 30 cc. of alcohol was added to the mixerand the mixing continued for two minutes. With the mixer running 68 gms.of a liquid phenol-formaldehyde bonding resin was very slowly addeduntil the mixture was complete, about eight minutes. Each particleshould be coated with the liquid, and the resulting powder should spillfreely without balling up. With the mixer still running, 204 gms. of adry powdered phenol-formaldehyde resin was added gradually, and mixingcontinued for about eight minutes. The treated powder was now ready forpouring freely into the mold, and the mold could be vibrated or rappedwith a hammer to pack the particles into all crevices. It was now readyfor curing to produce the finished mold. The mold was heated to 340 F.forthree hours. After removal of the die from the mold, the die wasreturned to the oven for another three hours.

If desired, the die 40 may consist of a window plate 42 which isattached directly to a rectangular die box (not illustrated). Variousforms of reinforcing can be utilized in the die box, such as reinforcingrods buried in the resin-sintered mass, and a rectangular piece ofexpanded metal grid added to the surface of the mass to add structuralstrength. Likewise, when desired, the spherical particles may extendflush with the surface of the Window plate 42 and margin straps may beassembled onto the plate to form the outline of the egg carton to thethickness desired. This marginal thickness in the window plate 42 isillustrated at 41 in FIG. 1.

The finished die assembly 0 is now ready for molding cartons. A typicalpulp furnish that may be used is Percent blank news 5} 15 bleached kraftnewspaper P 10% bleached kraft deinked The consistency is 60%, molding.time 7 seconds, utilizing a vacuum before molding of 5 Hg and 18" Hgafter molding. A transfer air pressure'of 50 p.s.i. is used and thecartons are dried on a plaster drying form in an oven at 350 F. fortwenty-five minutes.

The curing time recited heretofore for sintering the resin and sphericalparticles is a function of the weight and cross-section of the articlebeing formed, and should be varied accordingly.

The proportions of resin to spherical particles should be maintainedsuch that the resulting material is as rich in resin as possible and yetcapable of freely flowing like dry sand. Various types of sphericalparticles may be utilized as well as various types of bonding agents.

This method of preparing dies has many advantages over the presentlyused method utilizing wire woven cloth. Experimental and pilot plantwork can be accomplished with much less time and expense where it isnecessary to study design changes and modify the molding dieaccordingly. Screenless dies, in accordance with the present invention,are easily reconstructed in different dimensions with altered designfeatures incorporated. Temporary molding dies may be quickly and cheaplyprepared where only a few product samples are required. The screenlessmolding dies in accordance with the present invention may be made atless than half the expense of conventional screened molds. Maintenanceof screenless molding dies described in this application is simplified.When a unit becomes damaged it may be scrapped and incur less expensethan an overhaul of a conventional screened molding die. The appearanceof the product made on a screenless molding die in accordance with thisinvention would be noticeably improved. The surface of the product isuniform and bears no marks of the screens or the seams.

It will be obvious to those skilled in the art that various change maybe made without departing from the spirit of the invention and thereforethe invention is not limited to what is shown in the drawings anddescribed in the specification but only as indicated in the appendedclaims.

What is claimed is:

1. A method of making a porous pulp molding die having an exterior openfaced, contoured molding surface provided with a peripheral portionwhich comprises preparing a window opening extending through a fiatmetal plate, said opening conforming to the shape of the peripheralportion of the desired molding surface, attaching a reinforcing gridarrangement below the window opening of said metal plate, preparing amale master pattern mold conforming to the contours of the desiredmolding surface, placing said metal plate in inverted position, with thegrid arrangement extending upwardly over said male master pattern sothat the contours thereon are located over said window opening, pouringphenolic resin coated spherical bodies onto said male master pattern toa thickness covering the contours of said pattern as well as saidreinforcing grid arrangement, said spherical bodies having a diameter ofapproximately 3 to 50 mils and being made of a material which is hard,non-porous and stable at the curing temperatures of said phenolic resin,sintering said phenolic resin coated bodies together into a compositeporous structure by heating until said resin is cured followed bycooling to bond said spherical bodies together at portions of theirperipheries by the cured resin leaving voids and pores for the passageof liquid, and separating said male master pattern from said resultingdie.

2. In the method of claim 1 wherein said spherical bodies are glassbeads.

3. In the method of claim 1 wherein said spherical bodies are metal.

4. A method of making a porous pulp molding die having an exterioropen-faced contoured molding surface,

which comprises preparing a male master pattern mold conforming to thecontours of the desired molding surface, enclosing the pattern moldwithin side plates, pouring phenolic resin coated spherical bodies ontosaid male master pattern to a thickness covering the contours of saidpattern, sintering said phenolic resin coated bodies together into acomposite porous structure by heating until said resin is cured,followed by cooling to bond said spherical bodies together at portionsof their peripheries by the cured resin leaving voids and pores for thepassage of liquid, and separating said male master pattern from saidresulting die.

5. In the method of claim 4 wherein said spherical bodies have adiameter of approximately 3 to 50 mils.

6. In the method of claim 4 wherein said spherical bodies are glassbeads.

7. In the method of claim 4 wherein said spherical bodies are metal.

References Cited in the file of this patent UNITED STATES PATENTS2,064,435 Loefiier Dec. 15, 1936 2,359,201 Chaplin et al Sept. 26, 19442,460,242 Renaud I an. 25, 1949 2,632,922 Kish Mar. 31, 1953 2,806,509Bozzacco et a1. Sept. 17, 1957 3,001,582 Kindseth et a1 Sept. 26, 1961

1. A METHOD OF MAKING A POROUS PULP MOLDING DIE HAVING AN EXTERIOR OPENFACED, CONTOURED MOLDING SURFACE PROVIDED WITH A PERIPHERAL PORTIONWHICH COMPRISES PREPARING A WINDOW OPENING EXTENDING THROUGH A FLATMETAL PLATE, SAID OPENING CONFORMING TO THE SHAPE OF THE PERIPHERALPORTION OF THE DESIRED MOLDING SURFACE, ATTACHING A REINFORCING GRIDARRANGEMENT BELOW THE WINDOW OPENING OF SAID METAL, PREPARING A MALEMASTER PATTERN MOLD CONFORMING TO THE CONTOURS OF THE DESIRED MOLDINGSURFACE, PLACING SAID METAL PLATE IN INVERTED POSITION, WITH THE GRIDARRANGEMENT EXTENDING UPWARDLY OVER SAID MALE MASTER PATTERN SO THAT THECONTOURS THEREON ARE LOCATED OVER SAID WINDOW OPENING,POURING PHENOLICRESIN COATED SPHERICAL BODIES ONTO SAID MALE MASTER PATTERN TO ATHICKNESS COV-